Bob Supnik for his
Computer History Simulation Project. His PDP-11 simulator in the
simh suite is the best
open source PDP-11 simulator. It is the authoritative behavioral model
of various PDP-11 processors written in C.

Tristan Gingold for ghdl,
the best and most complete open source VHDL simulator.

Jiri Gaislers VHDL design approach (see
paper and
presentation).
Many w11 modules are implemented in Jiri's two-process design methodology
and make heavy use of VHDL records, within entities but also in interfaces.
The best example of this methodology is Jiri Gaislers's
LEON3 implementation,
another is for example the
MB-Lite core
on OpenCores.

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